BLKREPLAY(1)

📦
version 1.0 · 2 versions
, in debian bookworm, debian trixie, ubuntu jammy, ubuntu noble

💖 BLKREPLAY(1) 💖

okay so bestie, pull up a chair, we're talking about blkreplay from section 1 of the manual — the block device testing and benchmarking tool that's genuinely kinda iconic 🔥

✨ NAME ✨

blkreplay — block device testing and benchmarking tool, no cap 💅

🌸 SYNOPSIS 🌸

blkreplay [options] device

that's it. that's the whole vibe. one device, a bunch of options, and a whole lot of I/O 🦋

💜 DESCRIPTION 💜

so blkreplay is a utility that drives the block layer of your operating system while it measures latency and throughput of I/O operations, so you can go visualise all that later 📊✨

it can create artificial loads (random read-write sweeps, various kinds of overload tests, the whole dramatic repertoire) OR it can replay natural loads that were recorded by blktrace or a similar utility running on actual production servers 👑

and like, what's it for? so many things bestie:

  • testing physical hardware
  • comparing different brands of hard disks or RAID controllers
  • evaluating the effect of SSD caching
  • comparing different block level transports like iSCSI vs Fibrechannel
  • and so on and so forth 🎀

one thing you gotta know: blkreplay parses the load data from stdin. so if you wanna create load data from blktrace output, use the conv_blktrace_to_load.sh script. periodt 💫

🎀 OPTIONS 🎀

🌈 Influence replay duration

  • --replay-start=val — start offset, in seconds. 0 = from_start 🏁
  • --replay-end=val — end offset, in seconds. 0 = unlimited 🌌
  • --replay-duration=val — alternatively, specify the end offset as a delta (yes, a different way to say the same-ish thing, she contains multitudes) 🧚
  • --replay-out=val — start offset used for output, in seconds 📤
  • --start-grace=val — start after a grace period for filling the pipes, in seconds ⏳

💅 Handling of conflicting I/O requests

  • --with-conflicts — conflicting writes are ALLOWED. this means damaged I/O, bestie. it's giving chaos 😭
  • --with-drop — conflicting writes are simply dropped 🗑️
  • --with-partial — partial ordering by pushing back conflicts. this one is the default 👑
  • --with-ordering — enforce total order in case of conflicts 🔒
  • --strong=val — mode between 0 and 2, see docs. default is 1 💪

🦋 Replay parameters

  • --threads=val — parallelism. default is 1024 🧵
  • --fill-random=val — fill data blocks with random bytes, as a percentage. default is 0 🎲

⭐ Verification modes

  • --no-overhead — verify is OFF. this is the default 🙈
  • --with-verify — verify on reads 👀
  • --with-final-verify — an additional verify pass at the end 🏁
  • --with-paranoia — re-read after each write. this destroys performance, and I mean obliterates it 💀

🫶 Convenience

  • --verbose=val — increase verbosity, show additional INFO: output 🗣️

🔥 Expert options (DANGEROUS)

okay bestie, this is the expert section. the manpage literally put DANGEROUS in caps. read every line, fr fr 🙏
  • --o-direct — use O_DIRECT. this is the default 💾
  • --no-o-direct — don't use O_DIRECT. this delivers FAKE results 😭
  • --o-sync — use O_SYNC 🔄
  • --no-o-sync — don't use O_SYNC. this is the default 🚫
  • --dry-run — don't actually do I/O, just measure internal overhead 🧪
  • --fake-io — omit lseek() and tags, so even less internal overhead 🎭
  • --simulate-io=val — delay value for I/O simulation, in timespec sec.nsec format ⏱️
  • --ahead-limit=val — limit pipe fillahead, in realtime sec.nsec 🚧
  • --fan-out=val — only for kernel hackers. default is 4 🤓
  • --no-dispatcher — only for kernel hackers 🔧
  • --bottleneck=val — max number of requests on dispatch 🍾
  • --speedup=val — speedup / slowdown by a REAL factor. default is 1.0 ⚡
  • --mmap-mode — use mmap() instead of read() / write(). [NYI] — not yet implemented, so don't get your hopes up 🫠

👑 AUTHORS 👑

blkreplay was written by Thomas Schoebel-Theuer. this manual page was created from blkreplay documentation by Andrew Shadura. absolute legends, both of them 🫶

Copyright 2009-2012 Thomas Schoebel-Theuer

💫 SEE ALSO 💫

and that's the whole page, bestie 💖 this one's dated 2021-01-06 and it lives in section 1 as BLKREPLAY(1) — go forth and benchmark responsibly, mwah 💅✨🎀

📦 where this page comes from